Shimano GRX front derailleur compatibility

Question

I'm planning to upgrade my existing Shimano road 11sp groupset with a GRX 46/30 crankset.
According to Shimano, this means I need to use the FD-RX810 front derailleur. Apparently the 10sp FD-RX400 won't work.
However, I can't see why not. One answer to this question suggests that the pull ratio should be identical, but doesn't go as far as explicitly stating that it'll work. Other than pull ratio, I cannot see any other issue.
The FD-RX810 is currently unavailable where I live (presumably due to Shimano's supply chain issues), so can I just buy an FD-RX400?

JoeK · Answer

The 11sp derailleur cage is designed for the externally narrower 11sp chain. therefore the shifting will be less precise using an 11sp chain with a 10sp front derailleur

rvil76 · Answer

Chainline is shifted by 2.5 mm outside on the GRX crankset (compared to a road one), so the road front derailleur may not reach the outer ring on the GRX crankset.

Shimano GRX front derailleur compatibility

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